The publisher
Champagne Books is offering 50 percent off on its e-books through July 31; the code is
xmasEjuly.
I just came across this site by happenstance; I don't know anything about the publisher, but it looks like there's a nice selection of both print and electronic titles (PBs are 20 percent off throught July 31 with code
xmasPjuly). The FAQs says the e-books are available in PDF/LIT/PRC/HTML/EPUB formats--no mention of DRM.